1. Field of the Invention
The present invention relates to a solid electrolytic capacitor comprising a plurality of integrally molded capacitor elements.
2. Description of Related Art
An example of the solid electrolytic capacitor comprising a plurality of integrally molded capacitor elements is illustrated in FIGS. 13 and FIG. 14. In this solid electrolytic capacitor, a plurality of capacitor elements 1 are disposed side by side on a cathode terminal 2. Each of the capacitor elements 1 comprises a dielectric film 5, a cathode layer 6, and a cathode lead-out layer 7, which are formed in succession on the surface of an anode body 4. The anode body 4 is made of a valve metal and is provided with an anode lead member 3, which serves as an anode lead part. The anode lead member 3 is implanted on one end face of the anode body 4. Each of the cathode lead-out layers 7 of the capacitor elements 1 is connected to the cathode terminal 2, and each of the anode lead members 3 is connected to an anode terminal 8. The plurality of the capacitor elements 1 is covered and hermetically sealed by a housing 9 made of a synthetic resin, such as an epoxy resin.
The cathode layer 6 may be formed of a conductive inorganic material, such as manganese dioxide, or a conductive organic material, such as a TCNQ complex salt and a conductive polymer. The cathode lead-out layer 7 may be layers of, for example, a carbon layer and a silver layer formed in succession.
The cathode terminal 2 is bent in a step-like shape. After applying a conductive adhesive onto its lower step, and the plurality of the capacitor elements 1 are mounted thereon (Japanese Published Unexamined Patent Application No. 5-234829, for example).
The above-described configuration can achieve reduction in ESR (Equivalent Series Resistance) because it has a plurality of separate anode bodies 4 and accordingly the distance at which the current flows from the interior of the anode body 4 through the cathode layer 6 to the cathode terminal 2 is accordingly short. Moreover, since an additional effect of ESR reduction can be obtained because of the parallel connection of the capacitor elements 1, the completed product of the solid electrolytic capacitor attains good high frequency characteristics.
When the plurality of capacitor elements 1 are covered and hermetically sealed by the housing 9, the outside surfaces of the plurality of capacitor elements 1 are brought under a pressure force if, as described in JP 5-234829A, injection molding is carried out using a resin material such as an epoxy resin without providing a gap between the capacitor elements 1. The term “outside surfaces” means the outermost surfaces of the plurality of the capacitor elements 1; in the case that two capacitor elements 1 are arrayed on the cathode terminal 2, the surfaces of the capacitor elements 1 other than the side surfaces of the capacitor elements 1 that face each other are the outside surfaces of the capacitor elements 1. Due to the pressure force to the outside surfaces, the cathode layers 6 and the cathode lead-out layers 7 are compressed and damaged in the side surfaces facing each other of the capacitor elements 1. This has been a cause of deterioration in the capacitor's initial electrical characteristics such as ESR and LC (leakage current) and deterioration over time under a high-temperature, high-humidity environment.
Demands for smaller size, larger capacity, and lower resistance in solid electrolytic capacitors such as described above have been increasing. If the capacitor elements 1 are arranged on the cathode terminal 2 at a wide interval, the compression between the capacitor elements 1 in the injection molding can be prevented and the foregoing issue can be resolved. However, such an arrangement is undesirable because the outer dimensions of the solid electrolytic capacitor will increase.
Moreover, the capacitor elements 1 are placed under uneven loads by a pressure exerted from outside or a pressure originating from expansion of the resin in a high-temperature environment after the solid electrolytic capacitor is completed. This has also been a cause of deterioration in electrical characteristics of the solid electrolytic capacitor.